


no heartbeat, no problems

by CkyKing



Series: be gay, do (war) crimes [1]
Category: Fire Emblem Series, Fire Emblem: Fuukasetsugetsu | Fire Emblem: Three Houses
Genre: Alternate Universe - Canon Divergence, Gen, both with and without magic, byleth is a walking disaster, garreg mach isn't ready, jeralt is very proud, parenting, sothis' presence is acutely felt but not yet seen, the greatest battlefield of them all, their unlucky enemies not so much
Language: English
Status: In-Progress
Published: 2020-01-28
Updated: 2020-03-26
Packaged: 2021-02-27 07:33:36
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings, Graphic Depictions Of Violence
Chapters: 3
Words: 4,179
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22453474
Author URL: https://archiveofourown.org/users/CkyKing/pseuds/CkyKing
Summary: So, what do you get when you mix the child of the most renowned knight in recent history, a scary proficiency with weapons and an even scarier affinity with offensive magic?A heart attack, probably.A real fucking mess, most definitely.[Byleth's growth through a series of lessons―from fists to magic, nothing's out of your reach if you're spiteful enough]
Relationships: Jeralt Reus Eisner & My Unit | Byleth
Series: be gay, do (war) crimes [1]
Series URL: https://archiveofourown.org/series/1615672
Comments: 13
Kudos: 106





	1. hazardous reactions

Byleth was, in his own modest opinion, a pretty simple person. He liked good food, animals, warm places to nap on and training with his father and his men. Easy and straightforward, right?

_Wrong._

What Byleth failed to consider was that _nothing_ about the Blade Breaker and his crew could be described as “easy” or “straightforward”. 

(And that, of course, included himself, not that he’d realize it for a long, long time.)

***

He doesn’t pick up spellcasting as much as _it_ chooses _him_ and keeps on interfering with his life no matter how hard he tries to drop it like the hot potato it is. He is his father’s son to the bone and trusts steel more than some unknown energy supposedly coursing through his veins and sparking to life at the most inopportune times. 

Not that he is blind to how useful and deadly black magic could be, far from it. It is just that, even as a small child, Byleth’s self-image is such that it would (and successfully, at that) make an adult several times his age weep in envy, and nowhere within it is magic but a footnote, the rest of it filled with images of his father’s lance, sharp and deadly, or the deceptively subtle length of the knife Jeralt had commissioned specifically for him.

To his annoyance ― and the hilarity of his father’s subordinates ― fire is the element that comes to him the easiest; which, he had to admit, was useful in the frozen hellscape that is the Kingdom. In the Alliance with its abundance of forests and people and plains, all of them as flammable as the others? Not so much.

So, Byleth does as Byleth is wont to do when faced with a problem ignorance couldn’t fix: kick it in the face, ride it to the ground and find the sweet spot between the third and fourth rib.

Which is to say that if he is to be burdened with becoming a glorified campfire, he is going to _own it._

Jeralt can only look on with a particular mix of dread and resignation ― the kind usually reserved for encounters with wild nesting wyverns or particularly decrepit, thus even more self-important that usual, nobles ― and pray to all the saints he knows and all those he doesn’t that this doesn’t come back to bite him in the ass.

Goddess knows he loves his kid and would do anything for him, but that child could be so _bloody single-minded_ sometimes. Too much like his mother in that aspect, but the sheer pig-headness in pursuing something he wants?

Yeah, he only has himself to blame for that one.

***

Byleth takes back everything bad he ever said about dark magic.

Who knew setting things (and people, don’t forget the people) on fire could be so _therapeutic_?

With fire now in his arsenal, no one, not even archers or winged opponents are safe from him. Being thought even more deadly than usual shouldn’t feel so rewarding, especially at his age, but honestly? Expectations can kiss his ass and hop directly down into Helel where a lovely bonfire of _i-don’t-give-a-fuck_ is waiting for them with a side-dish of _fucking-watch-me_.

What can he say, growing up with mercenaries gives one a very particular outlook on life that includes such things as: a complete disregard for widely acknowledged forms of combats, zero tolerance for bullshit when money’s involved and an early grasp of the type of vocabulary that’d make even an Almyran warlord blush.

By now, he’s grown out of the pale hair and eyes that earned him the title of “Ashen Demon” (and those who knew what else was involved in his baptism by fire are either dead or not talking) but strangely enough, he notices a sharp uptick in use once he starts dropping down into battle wreathed in flames and slinging boulder-sized fireballs at horrified bandits.

Honestly, people are so damn predictable. “Oh gods, oh fuck, is that kid _on fire? and wielding a sword?_ Why is its face so still? You know what, let’s call him the Ashen Demon!” Is it too much to ask for some creativity?

At least they had reasons to when he was a child and looked so pale his dad refused to let him go anywhere without a cloak but what’s their excuse now?

Which is why Byleth starts digging into the grittier parts of white magic―and why Jeralt gives more than a few shopkeepers heart failures by looming threateningly until they break and give him whatever grimoires they had gathering dust in hope of a wealthy patron ― read: sucker ― at a _preferential_ price. 

(Let no one say that Jeralt is not a supportive father.)

Aah, spite, the greatest motivator this side of Fodlan.

If they wanted a demon, they’d _get one._

***

If people were scared when Byleth started wielding fire like it’s going out of fashion, they are fucking _terrified_ when he adds his bastardized version of faith magic to the mix.

Bastardized mainly because, as stoic as he normally comes off as, Byleth likes a little more _oomph_ to his fights that what traditional magic offers and Papa didn’t raise no quitter, thank you very much.

Papa apparently didn’t raise no healer either, because the one time he tried healing someone, the results were―well, let’s just say _terrible_ and leave it at that. At least they got an awesome scar out of it, so he’ll count that as a win.

(See, people take one look at Byleth and thinks he’s always calm and composed because he struck the genetic lottery when it came to poker face: not too bitchy, just a touch judgemental and as _transparent as a brick wall_. Except everyone who actually knows him can tell tell you that; one, he has many opinions and not saying them does not mean he isn’t judging you for your stupidity and two, that he didn’t ask for _your_ opinion in the first place and doesn’t care except if your name starts with Je and ends with Ralt.)

So, what do you get when you mix the child of the most renowned knight in recent history, a scary proficiency with weapons and an even scarier affinity with offensive magic?

A heart attack, probably.

A real fucking mess, most definitely.

But that’s alright, his dad didn’t become the Blade Breaker by sitting pretty and avoiding battles. That’s most likely how he managed to raise to raise Byleth into a semi-functional...human...being(?) after all, which, kudos to him, because fatherhood is the one battlefield he refuses to step a foot onto for all of the respect and admiration he has for his father.

So, the Ashen Demon: from little spun-glass kid to fiery teenager to haloed not-quite-adult.

At least now, he can picture turning their sprawling mansion into the next coming of Ailell the next time a noble calls him that to his face and act like they own him.

Aura, in the hands of an experienced white mage, is deadly. In his hands, it topples right over into _horrifying_ because light _shouldn’t bend this way,_ just like Nosferatu isn’t supposed to leave the target looking they went a round or ten with a sloth of Duscur bears.

_“Physician, heal thyself”_ indeed.

***

Of course, that is not to say that Byleth gives up his more physical means of defending himself, far from it, in fact.

For all that he favors his mother’s willowy build over his father’s bulkier one (but _with none of their height goddamn it_ ), he can and _will_ knock you into next moon by sheer force of will if nothing else.

Byleth’s height has always been a sore point to him, not that he’d admit it to anyone except for his father who laughed himself silly (and may have shed a tear or two, not that he’d admit it) the first time his tiny son put his hands on his hips and glared up at him like he’d been mortally offended. 

Which is why, from age _presumably_ two to six ― damn Jeralt for being such a cagey bastard ― Byleth could be found either sitting on his father’s shoulders or using his arm as a perch to look around like the magpie he secretly is. Coincidentally, it is around that time that Jeralt started sporting his customary braid, which is rumored to have started as one of Byleth’s means to distract himself while surveying the world from the safety of his father’s arms. Not that anyone would ever say it to his face if they fancied their ability to digest solid food; or had the survival instinct of a drunk salmon, whichever applies.

So, a less-than-impressive-height, a temper like a stiletto and a mind at least twice as sharp: a wonderfully explosive mix that Jeralt saw coming from a mile away ― would be hard not to, after being in the service of someone like Rhea for who knows how long ― and _further weaponized like the madman he stoically pretends not to be._

As Byleth would later put it to a disturbingly starry-eyed Caspar: “if they don’t fall, hit them harder.”

Of course, there is a great deal more to it than this, but it’s still one of the driving principles behind Byleth’s hand-to-hand. That wasn’t always the case though.

Originally, the saying, first uttered by Jeralt to his attentive child was: “if you can’t hit hard, then hit smart.”

This went right out of the window and died a long and agonizing death when he realized that common sense _just did not apply to his son_. 

How so, you may ask?

Well, picture a mercenary. Let me guess, probably tall, unkempt facial hair, a scar or ten and an even scarier look? Your lack of imagination notwithstanding, you would be mostly correct.

Now, imagine a, hmmm, let’s say a six year old, the smallest one you can. Yes, six year old should be about right. Pale hair and eyes and even paler skin, pearl and ivory and the finest porcelain; a pretty cute, if blank, kid all things considered.

And for the final part: imagine the later punching the former. What happens?

Nothing, right?

Well, you (and Jeralt whose train of thought followed the same vein) would be utterly and irrevocably _wrong_.

Because when that happened, the result was a wheezing mercenary whose self-esteem bruised just like his kidney where a dutiful Byleth followed his father’s step-by-step instructions on the art of throwing a proper punch; and said-father’s gobsmacked expression at how such a tiny frame could house enough strength to make a grown man _cry_.

And then Jeralt remembered House Blaiddyd and made the executive decision to restrain hand to hand training with Byleth to himself and a few select teachers who wouldn’t run screaming when faced with a child who could probably break their spine in several places if he put his mind to it.

Pair that with speed, the element of surprise and the kind of dirty tactics and cutthroat (literally) moves Dagdans affectionately call unarmed combat ( _generously taught_ ― bribed and blackmailed into ― by one of Jeralt’s many acquaintances) and you get one scary motherfucker.

So you see, when magic starts leaking from Byleth like the angriest sieve in existence, he is not even surprised anymore.

He’s still damn proud when his kid browbeats it into following his orders though; just like how he managed to wrap their ragtag group of mercenaries around his little finger.

The Blade Breaker and the Ashen Demon, what a pair, right?

They wouldn’t have it any other way.

***

**Notes for the Chapter:**

> so. finally decided to write something for fe3h. mainly because i am _tired_ of the lack of gay romance options so imma have to write it out myself i guess. the chaotic energy is strong in this one lmao


	2. accelerant

**Summary for the Chapter:**

> Wow, would you look at that, guess spears make great crutches when you’re in the process of _experiencing patricide via cardiac event._ Goddess’ tits, he’s way too old for this shit.
> 
> [Where Byleth makes a new friend and Jeralt is _concerned_ to say the least]

The wyvern is an accident...mostly.

(That is a bold faced _lie_ and Byleth isn’t fooling anyone)

Of course, trust Byleth to find the deadliest predator in all of Fódlan and decide “yes, that’s who I wanna make friends with, the giant overgrown lizard with a maw that’d make an entire battlefield jealous and a bite somehow worse than its already impressive bark. Oh, and did we mention the wings? Because there are very present, can bitch-slap you into next year if you’re not careful and make any attempts are running both futile and utterly laughable.”

Can you tell that Jeralt is _stressed out?_

Kid could probably outpunch the goddess and the star she rode in on? Eh, fine.

The magic and the constant bushfires? Useful, especially in the middle of the ass-backwards mountains the Kingdom call their backyard.

The thing with the light and the blood and the perversion of everything held sacred by all practitioners of faith magic was actually quite entertaining and _huh, seems like he’s still holding a grudge but oh well what can you do about it?_

He casually shoves aside the not-so-insignificant part of his brain that’s whispering about bones and organs and the exact force needed to crush both with a single blow because he is a professional dammit and _someone_ in this family needs to be the saner one and it isn’t looking good for Byleth so far.

But he draws the line at adopting the literal death on wings that’s— _is it chirping at his kid?_

Jeralt is already halfway across the clearing with his spear out by the time his brain catches up to the fact that there is a _baby wyvern wrapped around his child’s very fragile neck and it’s fucking_ chirping _at him._

Because the universe hates him, Byleth does not respond like any sane individual should – flinging the glorified lizard as far away as possible and booking it or staying still and praying to all the saints that it loses interest are both completely valid options so _why Byleth_ – and he laughs. _Laughs_ ; like doesn’t have the equivalent of an Almyran Death March wrapped around his neck. And reaches up to – shit, Jeralt’s heart is about to join Byleth’s in the beating-is-for-suckers category because he’s pretty sure he’s having a _heart attack_ – pet the blasted thing.

And it...lets him?

Wow, would you look at that, guess spears make great crutches when you’re in the process of _experiencing patricide via cardiac event._ Goddess’ tits, he’s way too old for this shit.

Byleth and his new...friend? pet?— _something_ both turn to look at him like he’s the one who’s out of his mind and dammit, they even tilt their head inquisitively at the exact same angle. He would find it endearing if he wasn’t too busy keeping his blood pressure from going through the roof.

Being the paragon of filial virtue that he is, Byleth goes right back to cooing over the juvenile mass-murder-waiting-to-happen instead of worrying about whether or not his old man is going to keel over. Which he has half a mind to do anyway because A) spitefulness is clearly a family inheritance and B) one thing you need to know, capital K, about wild wyverns is that if the child is within sight, then the mother is already in your blind spot plotting at least twenty ways to murder and spoon-feed you to said child.

There is a _reason_ why no one has ever managed to tame a wild wyvern in Fódlan since the time of Saint Cichol who single-handedly founded Wyvern Handling as it is still known and practiced today and that’s not for lack of trying in the, oh, _one thousand plus years since then._

And of course, because Byleth is determined to step on history’s face and drive a knife through its throat, they are not immediately carved apart like walking snacks while his lovely, _infuriating_ , son is busy petting the wyvern who seems to be...purring? Purring. Like this day wasn’t already strange enough.

He’s gonna need a fucking drink if he wants to get through this with his sanity at least partially intact.

***

After waiting for a tense half hour to fight for his and his child’s lives, Jeralt finally gives into the inevitable and adds “Beast Tamer” to the Byleth List of Impossible Things™ that seemingly gets longer every time he turns his back for five seconds.

Now that he has stopped scanning the forest around them for an angry mother dragon, he can finally take in the details about his son’s newest...friend, and he is struck by how _strange_ it is.

Wyverns, from his experience, usually come in earthy tones, green and browns and the rare ochres, all in the name of camouflage in their native forests and mountains. But this one is...colourful to say the least. Or rather, colour _le_ _ss_.

If he is honest, it reminds him of Byleth as a child; eerily so in fact. The pale, almost luminescent seafoam white of its scales; the wide eyes that look almost pupiless; even the sinuous length of its body, so unlike the usual drakeling stockiness is reminiscent of the blank child he’d seen grow up into the fiery, if only just in temper, not-quite-adult intent on breaking as many expectations as possible.

With his love for animals, he’d _known_ that Byleth would end up with one at some point or another, not just a mount like Jeralt himself favoured, but he’d at least _hoped_ that it would turn out a dog, or a cat, hell, even a Blessed Wyvern if it had come to that point.

Lady knew that Jeralt had enough contacts all over Fódlan to get one if Byleth was truly set on it, Church be damned.

If his kid wanted a wyvern, he’d get a damn wyvern, no matter what anyone else had to say.

The possibility of said kid taking things in his own hands and _taming one himself_ never crossed his mind, which, Jeralt thinks faintly as he watches Byleth slowly feed strips of venison to the content drakeling still draped around his neck like the deadliest of necklaces, he should have taken into account. He really, really should have.

  
Hopefully, Byleth will be distracted from breaking the laws of causality with another mouth to feed and—oh, who is he kidding, Fódlan is _doomed_.


	3. catalysis

**Summary for the Chapter:**

> Strong hands guide him down until he’s practically sitting on his father’s knee, a light suggestion he follows trustingly, gaze obediently turning away from his reflection to look up at his father instead. Jeralt’s smile, when he finally does, is long-suffering but amused; they have both grown used to the strange quirks of Byleth’s physiology by this point, and it is just another line to add to his mental registry of “ _Things I didn’t expected to have to deal with_ ” which, to his disbelief, keeps growing longer by the day. 
> 
> [Where Byleth discovers something new about himself and Jeralt should get a "Father of the Year" award for dealing with this]

“ _Mo leanbh_ ,” Jeralt sighs out despairingly when he finds Byleth prodding at his teeth, perched at the edge of a watering hole like a curious bird about to take flight.

_My child_ , he translates in his mind as his father kneels in front of him and gently tugs his hands down, his harsh Kingdom accent turned lilting and smooth around the flow of his birth tongue, the one he only uses with Byleth and that never fails to make him feel special; _loved_ , a little voice at the back of his mind corrects sleepily.

Strong hands guide him down until he’s practically sitting on his father’s knee, a light suggestion he follows trustingly, gaze obediently turning away from his reflection to look up at his father instead. Jeralt’s smile, when he finally does, is long-suffering but amused; they have both grown used to the strange quirks of Byleth’s physiology by this point, and it is just another line to add to his mental registry of _“Things I didn’t expected to have to deal with”_ which, to his disbelief, keeps growing longer by the day _._

So it is that work-calloused fingers turn his head to and fro, gently testing his cheeks for pain and discolorations before prying his mouth open, thumb pressed consolingly at the corner of Byleth’s lips. Small, meaningless phrases trickle out of him like water leaking from a sieve as he does so, comfort rusty but undeniably present as he digs through his foggy past for memories of his mother, of his father, for the harsh consonants and weather-beaten brogue of his childhood. Because his son may not complain, may be more skilled than people twice his age in some ways, but this does not make him any less of a child, any less deserving of a parent’s comfort.

Quick and clinical, he follows the lines of his teeth, prods at his gums in search of the telltale heat of infection and watches his face for any minute sign of pain or discomfort all the while. When Byleth does not so much as twitch, he probes deeper, running a finger again his palate this time, half-fearing a fracture or another ailment they’d be ill-fitted to treat without the help of a healer.

But what greets him instead is a peculiar give, a strange fold of flesh that briefly curves under the pad of his finger before a stinging pain replaces it, sharp and wholly unexpected.

Snatching his finger back and holding in a swear, he stares wide-eyed at his equally startled son, the reason for his earlier perplexity glinting dangerously in the diffuse light: a pair of fangs, ivory and viciously curved, sprouting right from Byleth’s mouth.

_Fucking hell_ , he thinks faintly, watching a bead of his own blood trail down Byleth’s fang, scarlet.

And he thinks back on the initial sting, at the impression of many more waiting under the yielding flesh of his son’s unformed palate.

The swears come back faster than the comforting words, but he thinks it’s warranted this time, what with his son growing a _whole new mouthful of fangs_.

_Goddess’ Tits, he needs a drink..._

But first, time to get a handle on the fangs. 

First order of business: **_does Byleth have venom?_ **

_...and the whole fucking bar as well for good measure._

***

The good news is, Byleth is not venomous.

The bad news is, _yet._

The thick yellow-red liquid that seeps from his fangs when he contracts the strange, snake-like muscles at the roof of his mouth is proof enough that he will eventually be able to poison people with a bite, if he so wishes.

At this point, he’s used to – but not quite inured – to his own peculiarity and spends an inordinate amount of time running his tongue against the folds of his fangs, testing their sharpness and even practices talking around them.

On the road between their various jobs, back against his father’s chest as Daemon rides on, he learns how to twist his tongue, how to work around his teeth until his words come out as crisp and clear as before they grew in, his father listening with a half-smile and eyes forever wary of ambushes.

The knowledge that he is different sits heavy in his mind, but like everything else, he eventually learns to shrug it off with a blank face and an even blanker demeanor, one more stone to the oddity that is his body.

At least, fangs are useful, he admits to himself, prodding at the soft flesh behind his teeth, feeling out for the indents of their sharper replacements, lying in wait just beneath the surface. 

Perhaps he will be as a snake, or even a wyvern, replacing them his whole life, trading them for better weapons with every turn of the year. 

Like the moon forever calls for the tide, so too, will he call for blood, for ivory and steel and all that gleams.

Byleth is a deathless thing, for all that he shares Jeralt’s warm colouring, the copper of his father’s birth mountains so rarely seen in Fodlan nowadays. His hair and eyes may darken with age, but in his mind, they are still white as bone, cool as snow, the immaculate banner that will one day give rise to the legend of the Ashen Demon. 

Is it any surprise then, that another sign of his otherness comes forth just as he starts to believe he will ever be normal?

And so he stops, because hope may spring eternal, but there is only so much disappointment he can take.

When the second pair comes in, wide and pointed like jagged trees on either sides of his tongue, he is not even surprised; only chalks it up to magic, or biology, or a strange mix of both.

How did it the saying go again?

“One for joy and two for sorrow, three _and-I-_ _don’t-fuckin-know_.” or some such meaningless drivel.

What he knows is this: he has two hands, deadly venom and magic crackling through his veins, and he is going to make the next person who lays hands on him _hurt._

If he grows claws next, that’ll just be one more thing to add to his arsenal and he’ll gladly take it.

All he knows is this: he will never be helpless again.

(his father’s hands, clinical but warm; _piscín_ , the point of it against his upper teeth, the fall of its second syllable in his mouth like the sour sweetness of late cherries on his tongue; the coarseness of his father’s hair between his fingers, silver and gold and all the warmest things in the world.

this is what they can’t take from him: he is loved, he is so, so _loved,_ and his father is coming for him. hope springs eternal but blood never lies. jeralt will always come for him, and as long as he draws breath, byleth will always have a home to come back to.

here is the spark: a heart that cannot beat and a soul that cannot rest.

part the two, and watch it all burn)

**Notes for the Chapter:**

> welp, seems like some seriousness snuck in at the end there. honestly though, being mercenaries is not in anyone's definition of a safe occcupations and trouble, was bound to come out of it at some point, earlier than you might expect in some cases ;)


End file.
